1. Field of the Invention
The present invention relates to a total traction control system which can be optimally applied in use for an automotive vehicle with both a first group of traction control system executing a traction control system based on a fuel-cut control and/or an ignition timing control, and a second group of traction control system executing a traction control based on a differential limiting torque control, a Wheel brake control, a throttle opening control, and/or a gear ratio control in an automatic transmission.
2. Description of the Prior Art
One such conventional automobile traction control system has been disclosed in Japanese Patent First Publication (Tokkai Heisei) No. 1-147127. In this conventional example, a traction control which is also known as "acceleration-slip control" is executed by utilizing a fuel-cut control according to which fuel-supply to a specified engine cylinder is stopped or an ignition-timing control according to which a preset ignition timing is retarded, so as to reduce an engine output power itself and consequently to suppress acceleration-slip owing to excessive traction applied to drive wheels. It is preferable to execute an output engine-power adjustment type traction control based on fuel-cut or ignition timing adjustment, since a high responsiveness of traction control can be obtained according to the fuel-cut control or the ignition-timing control. On some earlier vehicles, a fuel-increment control is made so as to change an air-fuel ratio at each engine cylinder from a stoichiometric air-fuel ratio towards a rich mixture during high engine load to enhance an output power of an internal combustion engine and to improve a driving performance of the engine. Additionally, the fuel-increment control is performed for the purpose of vaporization cooling in the engine cylinders and the catalytic converter in the exhaust system. Assuming that such vaporization cooling is executed simultaneously during traction control executed by utilizing fuel-cut control, unburnt fuel which is exhausted from engine cylinders subjected to vaporization cooling, tends to be re-combusted in the catalytic converter by incoming air flowing through at least one specified engine cylinder subjected to fuel-cut, thereby resulting in backfiring in the catalytic converter, i.e., overheating of the catalytic converter. As is well known, the catalytic converter must be properly heated to enhance catalytic action. Improper overheating would promote degradation of the catalytic converter. To avoid this, the above-noted Japanese Patent First Publication No. 1-147127 teaches the prevention of fuel-increment during traction control utilizing the fuel-cut control or the ignition-timing control. As set forth above, the conventional traction controller can effectively prevent the catalytic converter from being heated excessively, owing to backfiring therein. However, the conventional traction controller suffers from the drawback that the vaporization cooling in the engine cylinders cannot be executed during traction control even on engine high load. Particularly, in the event that the engine is held within a high-load range during sporty driving on high-friction roads such as dry pavements, acceleration-slip tends to occur repeatedly. Under such a condition, a traction control based on fuel-cut is made to suppress the acceleration-slip, while sacrificing an inherent driving performance of the engine, because a proper fuel-increment is prevented in the previously-noted prior-art traction controller. In order to ensure a satisfactory fuel-increment during sporty driving on dry pavements, another traction control different from the fuel-cut control and the ignition-timing control can be provided to suppress acceleration-slip. Since the differential limiting torque control, the wheel brake control, and the gear ratio control are achieved by adjusting a driving torque transmitted through the driving system to the drive wheels, these traction controls can be referred to as a "a transmitted driving torque adjustment type traction control". The four controls, namely the differential limiting torque control, the wheel brake control, the throttle opening control, and the gear ratio control has some advantages and disadvantages hereinafter described in detail.
(1) Throttle opening control:
The driving force applied to the drive wheel can be reduced at a reduction rate of 0% through 100%. The responsiveness of the throttle opening control is low.
(2) Wheel brake control:
The driving force applied to the drive wheel can be reduced at a reduction rate of 0% through 100%. There is a problem of undesired brake-pad wear.
(3) Differential limiting torque control or Gear ratio control:
The driving force applied to the drive wheel cannot be reduced at a satisfactory reduction rate.
On the other hand, the previously-noted output engine power reduction type traction control based on fuel-cut and ignition-timing adjustment exhibits a high responsiveness of the traction control and a high durability of the system. The output engine power reduction type traction control based on fuel-cut and/or ignition-timing adjustment also suffers from the drawback that a reduction rate of driving force applied to the drive wheel is limited within a relatively narrow range, as compared with the widest reduction rate of 0% through 100% obtained according to the throttle opening control and/or the wheel brake control.